Atmospheric Chemistry Program Seminar

Comparison of Common Vapor Pressure Estimation Methods through Modeling of Alkene OH·/NOx Systems
Emmaline Longnecker, ANYL 1st year, CU Boulder (1/2 seminar)
"Modeling of atmospheric reactions is an important tool in understanding the current and future impacts of human activity on the environment. Vapor pressure is a key parameter in modeling these reactions, as it largely determines the ability of a species to transition from the gas to particle phase. However, the vapor pressures of many atmospherically relevant molecules are still poorly constrained. In order to aid modeling efforts, several group contribution methods have been developed for estimating compound vapor pressures. The current study evaluates how four of these methods: SIMPOL, EVAPORATION, SPARC, and Nannoolal, impact the modeled predictions of secondary organic aerosol (SOA) yields for the reactions of C8-C14 1-alkenes with OH radicals in the presence of NOx. The models were created in the program KinSim and included detailed reaction mechanisms and branching ratios determined in several previous chamber studies by our research group, as well as gas-particle and gas-wall partitioning. SOA yields predicted using each of the four estimation methods were then compared to the measured values. The results of the models were variable, with the maximum discrepancies ranging from an underestimate of ~40% to an overestimate of ~30% compared to the experimentally determined mass yields. This variability exemplifies the impact of vapor pressure in modeling atmospheric reactions and indicates the need for further research in development of estimation methods."
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Redox-Active Coordination Complexes for Small Molecule Activation with Environmental Applications
Hanalei Lewine, ANYL 1st year, CU Boulder (1/2 seminar)
"Nitrate and nitrite are harmful pollutants resulting from the overuse of nitrogen fertilizers in agriculture. In Nature, denitrification converts these to lower-oxidation state nitrogen species, each step being catalyzed by a different metalloenzyme such as nitrate reductase. Synthetic systems that mimic these enzymes could convert NOx- to less harmful, and potentially useful compounds like nitrogen (N2) and ammonia (NH3). The highly versatile pyridinediimine (PDI) ligand has been successful in the reduction of these species due to the potential for incorporating redox-activity, proton-responsivity, and hemilability into the ligand scaffold. A new PDI iron complex featuring a hemilabile pendant phosphine shows reactivity towards nitrate and nitrate to selectively reduce to NO on a mononitrosyl iron complex (MNIC) will be presented."